Yeast not added. Although it may sound impossible ---- the yeast may not have been added initially! If in doubt add a second quantity.
Dead or damp yeast. An old yeast may have been used - adding a fresh yeast should restart the fermentation. Never use a yeast that has gone past the “best before” date. If in doubt, add
some fresh yeast as soon as possible.
Sterilising solution left in the fermenter. Where the equipment hasn’t been thoroughly rinsed after sterilising, there could still be traces of steriliser left behind that would kill the yeast.
Sterilising agent kills yeast as well as germs, and the solution should have been drained out of the jar before use. The equipment should not smell of steriliser when starting to use it.
Must (liquid) is too warm when yeast added.
This can kill or weaken the yeast. Add more yeast when the liquid is at 25C (77F).
Must (liquid) is too cold when yeast added This will not kill the yeast, but the liquid should be shaken well and moved to a warmer place. If the fermentation does not
start reasonably promptly, the must may become infected and spoilt. However, try using a Heating Tray or Brewbelt to guarantee a constant temperature.
Yeast nutrient added instead of yeast. This may turn the must black or dull grey/green. Yeast nutrient does not actually
contain yeast and yeast should be added as soon as possible. Although there is no need to add nutrient when making home wine from grape concentrates, it does no
harm and the colour will return to normal when fermentation starts.
Incomplete mixing of must (liquid). It takes quite a lot of stirring or shaking to dissolve sugar and mixing the grape
concentrate. If this is not done, dense syrup can settle to the bottom of the container and prevent fermentation. It is also the cause of the SG (hydrometer reading) apparently rising!
. Stir the fermenter again to ensure though mixing of the must.
Fermentation has already finished! In a warm situation, fermentation can finish in a few days, and inexperienced winemakers may not notice it. Check by tasting, or better still with a hydrometer. If
fermentation has finished, continue with the next part of the instructions.